This invention relates to a bidirectional communication system for use in carrying out bidirectional communication in a time division fashion by the use of a two-wire bus.
A conventional bidirectional communication system of the type described has been used in a user-network system of a two-wire bus having a first and a second end. A central terminator, such as a network terminator, is connected through the first end to the two-wire bus on the one hand and to a telephone network or the like on the other hand. A single terminal equipment, such as a telephone set, a personal computer, a facsimile facility, and the like is connected between the first and the second ends with the second end terminated by a usual passive terminator. Bidirectional communication is carried out between the central terminator and the terminal equipment by the use of the two-wire bus. More specifically, a down burst is sent from the central terminator to the terminal equipment through the two-wire bus on arrival of information from the telephone network while an up burst is transmitted from the terminal equipment to the central terminator through the two-wire bus on transmission of information from the terminal equipment. The two-wire bus is used in common by the down burst and the up burst. A collision between the down and the up bursts should be avoided on the two-wire line. Thus, switching between transmission and reception is necessary in the central terminator and the terminal equipment.
In addition, synchronization should be established in each of the central terminator and the terminal equipment each time when the communication is carried out.
Necessity of the above-mentioned switching and the establishment of synchronization restricts the bidirectional communication system of two-wire bus to one-to-one communication between the central terminator and the terminal equipment.
According to a CCITT recommendation, time division multiplex communication is preferably carried out in a four-wire bus communication system, not in the two-wire bus communication system.
Under the circumstances, it might be very useful to provide a two-wire bus communication system which can carry out time division multiplex communication.